Many different types of microelectromechanical (MEM) devices use one or more electrostatic comb actuators as motive sources. See, for example, U.S. Pat. No. 5,631,514 to Garcia et al which discloses a microengine that uses a pair of synchronized linear comb actuators as a power source. However, many problems exist with present electrostatic comb actuators which are generally considered to be low power, low output force devices.
Conventional comb actuators are disproportionate in size compared to other functional elements (e.g. gears, linkages, moveable assemblies, etc.) of MEM devices due to inefficient space utilization. Since a total substrate area (i.e. a die size) devoted to a particular MEM device is generally fixed by packaging constraints, the disproportionate area required for one or more comb actuators limits the area available for use by the other functional elements of the MEM device. As a result, the complexity of a MEM device utilizing a conventional electrostatic comb actuator will ultimately be limited by the area required for each actuator.
Another problem with conventional electrostatic comb actuators is that these devices provide a relatively low drive force limited to a few tens of microNewtons (.mu.N); and this level of drive force requires a relatively high operating voltage of up to 100 Volts or more. The relatively low drive force of conventional comb actuators limits their usefulness as power sources for many types of MEM devices.
Yet another problem with conventional electrostatic comb actuators is that a single-beam structure is commonly used; and this single-beam structure and one or more electrostatic combs supported thereon can easily be distorted due to slight asymmetries in a generated electrostatic field, or due to external loading. Such distortion can result in one or more fingers of an electrostatic comb bending or moving from a region of electrostatic stability to a region of electrostatic instability. This can result in binding of the comb actuator and limiting its range of motion. Permanent failure of the actuator can also occur as an electrical short circuit is developed between contacting fingers which are biased at different electrical potentials.
The compact electrostatic comb actuator of the present invention overcomes many of the above limitations in the prior art.
An advantage of the present invention is that a compact design is provided for an electrostatic comb actuator to conserve space upon a substrate or portion thereof, thereby providing for more economical fabrication and allowing the fabrication of MEM devices of increased complexity. This compact design results in part from the use of more-closely-spaced and thinner comb fingers, and in part from the use of restoring springs that require no additional space on the substrate beyond that reserved for the electrostatic combs.
Another advantage of the electrostatic comb actuator of the present invention is that this actuator can provide an increased drive force as compared with a conventional comb actuator.
A further advantage of the present invention is that a comb actuator is provided that operates at lower voltages than are possible with conventional electrostatic comb actuators.
Still another advantage of the present invention is that a comb actuator is provided with a more rigid structure that is less prone to distortion, thereby increasing the reliability of the comb actuator.
Yet another advantage of the electrostatic comb actuator of the present invention is that the actuator is electrostatically balanced to allow the use of thinner fingers with a closer spacing therebetween than is possible with conventional electrostatic comb actuators.
Still another advantage of the present invention is that an electrostatic comb actuator is provided with electrostatic shielding in critical places to minimize the effects of unwanted electrostatic fields, thereby increasing the available electrostatic drive power from the actuator and reducing any distortion of the structure of the actuator.
These and other advantages of the present invention will become evident to those skilled in the art.